In the prior art, 4-halocumenes are prepared by various methods described herein below:
As a process for the liquid phase chlorination of cumene, it has been common to conduct chlorination in the presence of Lewis acid catalyst such as ferric chloride or aluminium chloride by means of a chlorinating agent such as chlorine gas. However, such a process produces 2-chlorocumene as a major product and polychlorinated derivatives as by-products whereby it is difficult to produce 4-chlorocumene in good selectivity as high as at least 90%. Under these circumstances, there have been various researches for the development of catalyst to improve the selectivity for 4-chlorocumene.
In one method, chlorination of cumene was carried out using ferric chloride and chlorine gas which gives a mixture of cumene 1.8%, 2-chlorocumene 41.8%, 3-chlorocumene 1%, 4-chlorocumene 40.8% and polychlorinated cumenes 15% (Jpn. Kokai 5959,434 8453,434!).
In another method, chlorination of cumene was carried out with Cl.sub.2 in CCl.sub.4 in the presence of chemically modified silica catalyst for 2 h. In this case, the para/ortho ratios were slightly higher than those with FeCl.sub.3 (Chem. Lett. 11(1980)1423).
4-chlorocumene is also made by ring cumene with chlorine gas in the presence of Fe and FeS at 50.degree. C. After 2 h, the reaction mixture contained cumene 10.6%, 2-chlorocumene 28.8%, 3-chlorocumene 0.8%, 4-chlorocumene 56.6% and polychlorinated cumenes 3.3%. (Jpn. Kokai Tokkyo Koho JP 59,53,433 84 53,433!(Cl. C07 C25/02).
In another known method, chlorination of cumene over silica gel catalyst treated with nitrobenzene derivatives gives a mixture of 2-chlorocumene and 4-chlorocumene in a ratio of 1:2 ( Jpn. Kokai Tokkyo Koho JP 58 81, 443).
In another method, 4-chlorocumene is obtained in a selectivity of 75% by reacting cumene with chlorine by means of a SbCl.sub.3 modified catalyst (Jpn. Kokai Tokkyo Koho JP 60,125,25185,125,251!).
In the prior art, bromination of cumene is achieved using molecular bromine adsorbed on the surface of alumina without any solvent (Synth. Commn. 1992, 22(8), 1095). This method is disadvantageous since it is an adsorptive method.
In another method, cumene was brominated with N-bromosuccinimide (Ind. J. Chem. 1983, 22 B, 592).
The iodination of cumene was carried out by using I.sub.2 --Hg(NO.sub.3).sub.2 as an iodinating agent. The yields for iodocumenes and the selectivity for para-iodocumene were found to be 92 wt. % and 73%, respectively (Tetrahedron, 1994, 50(17), 5139).
However, these conventional methods are not satisfactory as a process for the production of 4-halocumenes because the selectivity for 4halocumenes is low (&gt;75%) in each case.
In view of the above mentioned low selectivity for 4-halocumenes in the prior art processes, it was found desirable during the course of the research work leading to the present invention to develop an improved process for the production of 4-halocumene in high selectivity from the halogenation of cumene using zeolite catalyst.